The present disclosure relates to planar patch antennas, and in particular to circular patch antennas having circular polarization.
Patch antennas, also referred to as microstrip antennas, are often used in radio frequency (RF) systems due to their small size, light weight, low profile, low cost, and ease of fabrication and assembly. Patch antennas typically include a conductive (e.g., metallic) patch portion separated from a large metallic ground plane by a low-loss dielectric spacer, such as quartz, alumina, ceramics, or other dielectric materials. The patch portion, separated from the ground plane by the dielectric, is typically energized via a RF feed. The patch portion and ground plane together form a transmission line that radiate electromagnetic fields from the edges of the patch. The resonant frequency (and hence the wavelength) of the antenna is dependent upon factors such as the size of the patch, the size of the ground plane, and the thickness and dielectric constant of the dielectric spacer.
Typically, such antennas utilize a patch portion that is approximately one-half of a wavelength of the frequency of operation. For instance, a patch antenna having a nominal operational frequency within the 2.4 gigahertz (GHz) Industrial, Scientific, and Medical (ISM) radio band may typically utilize a patch portion approximately 2.5 inches (6.35 centimeters) long, corresponding to approximately one-half of the wavelength of a 2.4 GHz signal in free space. As such, the size of the patch can make it difficult to integrate patch antennas into certain assemblies (e.g., sensors, transmitters, and the like) having size requirements that are less than the half-wavelength size of a signal at a specified nominal operational frequency (e.g., less than 2.5 inches in the case of a 2.4 GHz signal). Typically, patch antenna require electrically large ground planes (e.g., five times the size of the patch or more), thereby further impeding such integration efforts. Integration of patch antennas into certain assemblies, such as assemblies having metal housings, can further complicate matters by introducing proximity effects which can change the resonant frequency, as well as the bandwidth (BW).
Miniaturization efforts have been undertaken to help reduce the size of patch antennas. Resulting techniques have disclosed that the use of a dielectric spacer having a higher dielectric constant can decrease the size of the patch portion of the antenna, but at the expense of a reduced bandwidth. In addition, circular polarization can be helpful in operation in harsh operations. However, inciting circular polarization within a patch may typically require the use of a quadrature coupler that equally splits a RF power feed into multiple (e.g., two) phase-shifted signals that feed the patch at multiple points (e.g., opposite edges). Such quadrature couplers can be bulky in comparison to the patch antenna, thereby impeding miniaturization and integration efforts. Accordingly, it can be difficult to integrate patch antennas into assemblies having metal housings that are smaller than the half-wavelength size of a signal at a specified nominal operational frequency of the antenna.